Mobile satellite radiotelephone systems are being developed and deployed at many locations around the world. As is known to those having skill in the art, a mobile satellite radiotelephone system includes at least one satellite and at least one gateway that interfaces the mobile satellite radiotelephone system to other telephone systems such as wire telephone systems or mobile cellular radiotelephone systems. A plurality of satellite radiotelephones communicate with the satellite to provide mobile satellite radiotelephone communications. It will be understood that radiotelephone systems and other telephone systems can be used for voice and data communications, so that radiotelephones and other telephones can include terminals such as PCS terminals.
A major concern in mobile satellite radiotelephone systems is the reduction in the peak power consumption in the mobile satellite radiotelephones. In order to reduce the peak power required by the radiotelephone during transmissions to the satellite, it is known to use a narrow band Time Division Multiple Access (TDMA) waveform.
Many mobile satellite radiotelephone systems currently being planned or used, employ TDMA communications. In TDMA systems, multiple communications may operate on a single communications carrier by assigning non-overlapping time slots to each communication. In order to reduce the peak power requirements on the mobile satellite radiotelephones, it is known to use narrow band TDMA communications having frames with relatively few time slots. By providing relatively few slots for a given frame duration, each slot can be longer so that less peak power may be required for the communications. Battery peak power can thereby be reduced for the mobile satellite radiotelephones.
In contrast, in transmissions from the satellite to the mobile satellite radiotelephones, where the peak power issue is not as great a concern, wide band TDMA communications involving frames with more slots may be used. Wide band TDMA can increase the number of radiotelephones with which the satellite can communicate on a single carrier.
Accordingly, mobile satellite radiotelephone communications systems may use a non-symmetrical air interface, with narrow band TDMA used for mobile to satellite communications and wide band TDMA employed from satellite to mobile communications. A non-symmetrical air interface for mobile satellite radiotelephone systems is described in U.S. Pat. No. 5,539,730, Jul. 23, 1996 entitled TDMA/FDMA/CDMA Hybrid Radio Access Methods to Paul W. Dent and assigned to the assignee of the present invention, the disclosure of which is hereby incorporated herein by reference.
In geostationary mobile satellite radiotelephone systems it is also generally desirable to allow direct communications among the mobile satellite radiotelephones via the satellite without requiring the communications to pass through the gateway. These "single hop" communications can reduce delays which might otherwise be present if communications are relayed from one mobile satellite radiotelephone to another mobile satellite radiotelephone via the gateway. In order to effect single hop communications, the satellite generally includes rate conversion systems which convert received narrow band TDMA signals into wide band TDMA signals for transmission to the mobile satellite radiotelephones. Rate conversion in a satellite is described in application Ser. No. 08/581,110, filed Dec. 29, 1995, entitled "Time Compressing Transponder" to Paul W. Dent, and assigned to the assignee of the present invention, the disclosure of which is hereby incorporated herein by reference. Accordingly, the mobile satellite radiotelephones can transmit using narrow band TDMA and receive using wide band TDMA regardless of whether radiotelephone communications are being carried on with the gateway or among the mobile satellite radiotelephones themselves.